Asynchronous transfer mode (ATM) data transfer is a communication technology in which fixed-size packets of data, known as “cells,” are transferred between ATM switching devices (“switches”). ATM switches may be thought of as circuit oriented, low-overhead packet switches providing virtual circuits. The virtual circuits provide the basis for both switching and multiplexed transmission. Asynchronous time division (ATD) and fast packet switching are alternate terms which have been employed to describe similar transfer technology.
ATM networks transfer information using a cell format that typically conforms to formats adopted by the International Telecommunications Union (ITU). ITU-standard ATM cells have a 5-byte header field and a 48-byte payload field. The header field carries information pertaining to the transport and routing of an ATM cell through switching equipment in a communications network. The payload field is available to transfer user-data. User-data may be digitized video or audio, data from a computer application, or information provided by a higher layer communication protocol.
ATM cells are sent from originating network access equipment, typically located at a customer's premises, to an ATM network and from the ATM network to destination network access equipment, typically located at a second customer's premises. The ATM network provides end-to-end routing of the ATM cells.